Having too many kids is selfish and irresponsible
Kids are way too expensive and needy to just have a bunch of them. It's one thing to have like 1 or 2, but 4+ is just too much. There's no way average adults are able to give the time, money, and energy to that amount of kids.
I say this as someone who has three siblings. I spent most of my childhood sharing a small room with two of my siblings. We struggled with money quite a bit. My parents were always busy with work, so there wasn't much time to spend with us. My older sister had to take care of us a lot of the time.
I just don't like the idea of just saying screw it and having a big family, especially when it can mess with your childrens' lives. Yeah they can find a way to deal with it, but I think it's sad to force that type of life onto someone. You should be able to provide for your kids, whether it's your time, energy, or money. If too many kids would make that hard, and it most likely will, then you shouldn't have them.